Neuromonitoring And Neuroprotection Advances For Aortic Arch Surgery Part 2

Adding retrograde cerebral perfusion to DHCA has shown equivalent results to ACP with MHCA. A series of 376 patients undergoing hemiarch reconstruction for nondissecting disease, with short (average 22 minutes) HCA times, compared MHCA þ ACP with DHCA þ RCP and found no difference in 30-day mortality or stroke. 

Retrograde cerebral perfusion is a rare disorder that causes blood flow in the brain to flow in the opposite direction. This disease affects normal brain functions, including memory and thinking ability. While retrograde cerebral perfusion does affect memory, it can be overcome with proactive approaches.

First of all, maintaining a positive attitude is the most important thing. We should focus on the knowledge we have already mastered, which can stimulate our memory ability. At the same time, we should also actively learn new knowledge, which is also very helpful in enhancing memory.

Secondly, learning in a variety of ways can improve memory. For example, learning through different ways such as reading, listening to lectures, and watching videos can effectively improve memory. Different learning methods can fully stimulate our brains and help us remember knowledge better.

In addition, a healthy lifestyle is also very important. Exercising more, paying attention to your diet, and maintaining good sleeping habits can all help improve memory. These healthy lifestyle behaviors can improve the brain's ability to obtain oxygen and nutrients, thereby helping the brain function healthily.

In summary, although retrograde cerebral perfusion will affect memory, we can overcome it through an optimistic attitude, various ways of learning, and a healthy lifestyle. Improving memory can not only help us learn and master knowledge better but also improve our quality of life in daily life. It can be seen that we need to improve memory, and Cistanche deserticola can significantly improve memory, because Cistanche deserticola can also regulate the balance of neurotransmitters, such as increasing the levels of acetylcholine and growth factors. These substances are very important for memory and learning. In addition, Cistanche deserticola can also improve blood flow and promote oxygen delivery, which can ensure that the brain receives sufficient nutrients and energy, thereby improving brain vitality and endurance.

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However, MHCA þ ACP was associated with short cross-clamp and cardiopulmonary bypass times, as well as decreased transfusion requirements.27 

Similarly, a review of 8169 patients undergoing elective total arch replacement compared ACP (at 24.2
C) versus RCP (at 21.2
C) and found no difference in mortality, stroke, or transient neurologic disorder, although the use of lower temperatures with RCP was associated with longer intensive care unit length of stay.5 

A recent small prospective study of 20 patients undergoing elective hemiarch replacement randomized patients to either DHCA þ RCP (14.1
C-20
C) or MHCA þ ACP (20
C-28
C) and found no differences in incross-clamp, cardiopulmonary bypass, or HCA times. 

Clinical outcomes including stroke, transient ischemic attack, transient neurologic dysfunction, neurologic assessment by a neurologist, and neurocognitive deficits as assessed by a computerized cognitive assessment were all equivalent. However, magnetic resonance imaging (MRI) showed ischemic lesions in 100% of patients in the MHCA þ ACP group, but only 45% of the DHCA þ RCP group had lesions. Notably, the MRI findings were not detected by clinical neurologic examination or neurocognitive testing. 

The authors suggest the increased MRI findings could be due to either manipulation and clamping of the innominate or carotid vessels during cannulation for ACP or due to fundamental differences in embolic events between ACP and RCP.28 

These differences would support the use of RCP with deep HCA, but widespread adaptation for all aortic arch operations is limited by the commonly accepted notion that RCP offers less metabolic support for longer procedures, although circulatory arrest times in this study were short (19-21 minutes on average).5,29
Given the variability in patient population, disease type, circulatory arrest times, and even target temperatures between studies comparing hypothermia and perfusion strategies, relative outcomes are difficult to extrapolate to different populations, and trends must be identified from studies. 

DHCA alone has been demonstrated to be safe for short circulatory arrest times, but between 25 and 50 minutes, neurologic injury and mortality rates begin to climb. 

In general, expert opinion has favored using DHCA with RCP for intermediate-duration cases due to the ease of cannulation and theoretical retrograde flushing of embolic debris, while relying on either DHCA or MHCA combined with ACP for longer cases due to superior metabolic support.29,30 These neuroprotective strategies are summarized in Table 1.

FROZEN ELEPHANT TRUNK (FET)

Patients requiring concomitant intervention on the proximal descending aorta with the FET technique are a special group of arch patients. These procedures involve off-label use of devices, as none have Food and Drug Administration approval for this application. 

Given the known risk for spinal cord injury, we apply this procedure selectively to patients with visceral malperfusion or true lumen compression, particularly in younger patients. A pooled analysis of 3154 patients undergoing the FET technique found a 4.7% rate of spinal cord ischemia.31 These rates are consistent with our own center's experience with FET (4.1%).32
For complex distal aortic pathology, our preferred approach now is to debranch the innominate and left carotid arteries and replace the aorta to the level of the left subclavian artery (zone 2), creating a zone 0 proximal landing zone for later endovascular stent graft deployment with a left subclavian branched device or coverage of the left subclavian artery after a carotid to subclavian artery bypass. For extended coverage of the thoracic aorta, spinal cord–protective strategies may include cerebrospinal fluid drainage and monitoring of sensory- or motor-evoked potentials.33

SURGICAL TECHNIQUE AND CHOICE OF CANNULATION SITE
There is considerable variability in cannulation techniques among centers. Overall, there has been a decrease in the use of the femoral artery over the last 20 years due to a concern for showering emboli to the brain from the descending aorta. 

A 2014 meta-analysis of 4476 patients sought to compare peripheral cannulation (by femoral artery) to central cannulation (defined as direct aortic, innominate, right axillary, or right subclavian artery cannulation) for initiation of cardiopulmonary bypass. 

There was a significant association between central cannulation and decreased in-hospital mortality, as well as decreased permanent neurologic deficit.34 Right axillary artery cannulation has emerged as the preferred technique at many centers according to a study of the International Registry of Acute Aortic Dissection.9 However, this requires a separate skin incision, and often anastomosis of a side graft, which adds additional time and risks of both bleeding and lymphocele formation. At our center, we have favored direct aortic cannulation for most aortic arch repairs. 

This allows easy conversion to RCP via the SVC. In cases of acute dissection, we still favor direct aortic cannulation via a Seldinger technique, ideally using epiaortic and transesophageal echo for guidance into the true lumen. We have found excellent results in elective aneurysms with brief periods of DHCA alone (<15 minutes). For intermediate DHCA times (20-30 minutes), we often include retrograde cerebral perfusion. Our preferred approach for complex arch reconstruction is direct aortic cannulation, followed by arch debranching of the innominate artery and left carotid artery under DHCA, and then initiation of ACP via a branched graft (14 3 10 3 10 mm or 12 3 8 3 8 mm Vascutek; Terumo Aortic, Ann Arbor, Mich). 

ACP is typically delivered at 8 to 10 mL/kg/min flow via a limb that is Y-configured off the cardiopulmonary bypass arterial line. ACP may be initiated peripherally, by direct cannulation or by anastomosis of a graft side-branch, to the axillary artery or carotid artery.35,36 Alternatively, the innominate or left common carotid can be directly cannulated via an intrathoracic approach. No literature exists comparing outcomes with these different strategies, but we avoid direct cannulation of arch ostia due to concern for introducing atherosclerotic debris and air. 

A randomized controlled trial is underway comparing cerebral MRI findings in patients undergoing ACP via innominate cannulation versus right axillary cannulation.37 If axillary artery cannulation is employed with MHCA and ACP, then it is essential to monitor cerebral oximetry and arterial pressure with bilateral radial arterial monitoring lines. Anatomic studies have demonstrated that an incomplete circle of Willis may lead to inadequate perfusion of the left hemisphere in 14% to 17% of patients if the right axillary artery is used for cerebral perfusion.38 

A drop in left-sided cerebral saturation can be addressed with increased cerebral perfusion or direct cannulation of the left carotid artery with a separate cannula. Alternatively, the patient can be placed back on cardiopulmonary bypass with further cooling to DHCA.16 The topic of unilateral versus bilateral ACP remains a point of contention in the literature. It has been demonstrated that cerebral perfusion gradually declines with time, and does so heterogeneously within the brain, making certain regions more susceptible to ischemia. 

A meta-analysis of 3548 patients found low rates of neurologic injury for both DHCA þ RCP and MHCA þ ACP, but there were significantly longer perfusion times with bilateral cerebral perfusion, suggesting that for ACP times beyond 40 to 50 minutes, surgeons selected bilateral ACP.39 A 2017 study of 203 patients undergoing total arch replacement for type A dissection similarly found no significant difference between unilateral and bilateral ACP in terms of mortality or neurologic injury but found a nonsignificant reduction in mortality associated with bilateral ACP.40 

Subsequent analysis of this study has led some authors to favor bilateral ACP, given the minimal added risk.3 A 2019 retrospective review comparing unilateral versus bilateral ACP found an association between bilateral ACP and improved overall survival within the subgroup of patients requiring ACP durations of 50 minutes or longer.41 Another 2019 retrospective review comparing the 2 techniques similarly found no significant differences in outcomes, although 5-year survival was moderately improved in the group that underwent unilateral ACP.42 

These results may not be appropriately extrapolated to all patients undergoing aortic arch surgery, as there were underlying differences between the 2 groups of patients-those who underwent bilateral cerebral perfusion were more likely to undergo zone 2 or zone 3 arch replacement and had longer cross-clamp times, longer circulatory arrest times, and lower hypothermic temperatures. Regardless of whether unilateral or bilateral ACP is selected, we strongly urge monitoring bilateral cerebral oximetry intraoperatively to guide the adequacy of cerebral perfusion. 

Finally, if aortic arch debranching is performed, then the innominate can be perfused during the left carotid anastomosis, at which point bilateral perfusion can easily be initiated, limiting the duration of unilateral ACP.

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